This invention relates to a method of computing the capacity of a battery array made up of a plurality of rechargeable batteries connected in series, and controlling charging and discharging of the battery array.
A rechargeable battery capable of repeated charging and discharging is provided with a full charge detection circuit and an over-discharge protection circuit to prevent over-charging and over-discharging. As means of detecting whether a battery is fully charged, the voltage detection method which detects a rechargeable battery's voltage, the -DV method which detects a specified voltage drop from a peak rechargeable battery voltage, the temperature detection method which detects a rechargeable battery's temperature, and other methods are known. In addition, methods such as rechargeable battery voltage detection are widely known for incorporation into an over-discharge protection circuit.
Incidentally, in the use of rechargeable batteries as power sources, a plurality of rechargeable batteries are often electrically connected together in both series and parallel combinations for use as a battery array. In the case of a battery array, the capacity of each individual rechargeable battery and the performance of each rechargeable battery with charging and discharging shows some variation, and all rechargeable batteries do not react in exactly the same way. Consequently, even though observation of the over-all battery array shows no indication of a problem, it is possible that one part of the rechargeable battery array has over-charged or over-discharged and the battery array as a whole has been degraded.
To solve this problem, Japanese Patent Application HEI 7-335266 (1995) discloses a provision for bypass circuitry for each of a plurality of rechargeable batteries connected in series. However, for the case of a battery array used as a power source for an electric automobile, the number of rechargeable batteries connected in series is around two hundred, and circuit complexity becomes extreme.
Thus, it is an object of the present invention to provide a method of controlling charging and discharging of a battery array via a simple configuration that prevents over-charging and over-discharge of each component rechargeable battery of the battery array.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with a accompanying drawings.